1. Field of the Invention
The present invention relates to a congestion controller, and in particular, it relates to a congestion control system to control transmission traffic using a PAUSE frame when congestion occurs in an environment in which a plurality of Ethernet switches are connected.
2. Description of the Related Art
Conventionally, if congestion occurs in an Ethernet (Registered Trademark) network, a PAUSE frame defined by IEEE 802.3 is sent from a switch such as a switching hub, in which the congestion occurs, to inner switches, to thereby control input traffic (See Note 1).
FIG. 1 shows an example of congestion control using a PAUSE frame, and FIG. 2 shows a PAUSE frame format.
In FIG. 1, if congestion occurs in a link “α” on the transmission port side of a switch 1 (SW1), the congestion is detected by a threshold value of a buffer (queue) in the switch 1. Thereafter, in order to restrict the transmission traffic from inner switches 2-5 (SW2-SW5), the switch 1 sends a PAUSE frame to the switches 2-5. As shown in FIG. 2, the PAUSE frame sets, as the destination address (DA: Destination Address), a multicast address representing the PAUSE frame.
In a parameter field of the PAUSE frame, a timer value of Pause time, e.g., XX (ms) is set. If the timer value is 0, it represents that the PAUSE state is released and the transmission state is established. Other fields are the same as those of a typical Ethernet frame and are not discussed herein.
The inner switches 2-5 suppress traffic transmission to the outer switch 1 with which the congestion has occurred, for a predetermined time, based on the timer value included in the received PAUSE frame. If the node which receives the PAUSE frame is a terminal, transmission is suppressed temporarily based on the timer value, as long as the terminal has a NIC (Network Interface Card) which supports the PAUSE frame. When the PAUSE time is up, the transmission which has been suspended is resumed.
Note 1: Okabe Yasuichi <Detailed TCP/IP Protocol 9th Ethernet (No. 4) Flow Control and VLAN, Troubleshooting 1. Flow Control of Ethernet> [online] Oct. 2, 2001, Network Technology Lecture, [Searched on Sep. 9, 2002].
As described above, the PAUSE frame defined by IEEE 802.3 causes the switch 1 with which the congestion has been detected to request the inner switches 2-5 and lower terminals thereof to suppress transmission of all the traffic to the switch 1 for a predetermined time. However, such conventional operations have problems discussed below.
(1) Reservation of QoS (Quality of Service)
Because a PAUSE frame does not distinguish the kinds of traffic, e.g., audio and/or video traffic which have strict requirements on delay time and jitter, etc., and data traffic such as FTP (File Transfer Protocol) which has less strict requirements are treated equally. In particular, the QoS for the former traffic cannot be reserved.
(2) Improvement of Effective Throughput
Because transmission of all the traffic to the switch 1 from the switches 2-5 and lower terminals thereof is simultaneously suppressed for a predetermined time, there is a possibility that the PAUSE times lapse concurrently, so that congestion state and non-congestion state repeatedly appear. To improve the throughput, it is preferable that the amount of traffic be constant without fluctuating. The effective throughput cannot be improved by the conventional congestion control.
(3) Equality of Traffic
All the flows are stopped without identifying which flow causes the congestion, it is possible to allocate bandwidth equally to a plurality of existing flows. Namely, transmissions of traffic other than the traffic with which the congestion has occurred are equally suppressed.